"However, our findings show that vaccination alone is not enough to prevent people from being infected with the Delta variant and spreading it in household settings," Professor Lalvani added.
Researchers found that among 24 reported cases, Delta was seven-fold more likely to lead to vaccination breakthrough infections than non-Delta lineages.
High COVID-19 rate in 0-19 age group in India; frequent post-vax infections with Delta variant: Study
According to the WHO update, the study found an increased number of infections among the 0-19 age group and women, higher mortality and more frequent incidences of post-vaccination infections.
The delta variant has been identified in at least 180 countries, according to the World Health Organization.
Victoria state premier Dan Andrews said the decision came after a series of street parties, pub crawls and home gatherings over the weekend, as Melbourne reached a "tipping point" in the outbreak.
After eight new infections surfaced in the city, Victoria Premier Daniel Andrews announced that Melbourne and the surrounding areas of Victoria state will lockdown for seven weeks.
The ruling Communist Party is reviving tactics that shut down China: Access to a city of 1.5 million people has been cut off, flights canceled and mass testing ordered in some areas.
As recently as last week, the Centers for Disease Control and Prevention had defended its surprise decision in May that vaccinated people did not have to wear masks indoors in most circumstances.
Prevalence of Covid Delta variant among specimens sequenced over past 4 weeks exceeded 75 per cent: WHO
The COVID-19 Weekly Epidemiological Update reiterated that the Delta variant is expected to "rapidly outcompete" other variants and become the dominant circulating lineage over the coming months.
The health officials said that about 35 cases of the Delta variant of SARS-CoV-2, the virus that causes COVID-19, have been found in Sri Lanka so far.
A study by AIG Hospitals and Centre for Cellular and Molecular Biology in Hyderabad reported that the requirement of ventilatory support was low among vaccinated people who contracted Delta variant.
Authorities have locked down Ruili, blocking people from entering or leaving the city in Yunnan province and restricting residents in the urban area to their homes in a bid to contain the spread.
The woman in her 40s who died from the Delta variant first identified in India had not received the COVID-19 vaccination, had no underlying conditions and had been hospitalized in the Reno-Sparks area
The Delta variant has also been behind a steep upward curve in cases in the United Kingdom but that did not stop authorities easing restrictions for England's last-16 win over Germany on Tuesday.
He said the country also needs to be at the forefront and release the sequencing data in a week.